Multilayer polypropylene films and methods of making and using same

ABSTRACT

A method including forming a bilayer polymer film having an oriented polypropylene film and a metallocene-catalyzed polypropylene film wherein the metallocene-catalyzed polypropylene film has a seal initiation temperature of from 80° C. to 130° C. A laminate including a biaxially oriented polypropylene film, a metallocene-catalyzed polypropylene film, and a substrate, wherein the metallocene-catalyzed polypropylene film is disposed between the biaxially oriented polypropylene film and the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable

BACKGROUND

1. Technical Field

This disclosure relates to methods of preparing polypropylene films. More specifically, this disclosure relates to multi-layer polypropylene films for use in thermo-lamination applications and methods of making and using same.

2. Background

Synthetic polymeric materials, particularly polypropylene resins, are manufactured into a variety of end-use articles ranging from medical devices to materials packaging. Many industries, such as the packaging industry, utilize these polypropylene materials in various manufacturing processes to create a variety of finished goods including containers, packaging films for food packaging, thermo-lamination films for book covers, etc. For example, producing thermo-lamination films may involve extruding a layer of ethylene vinyl acetate (EVA) onto a plastic film (e.g., polypropylene) to form a bilayer film. Next, the EVA side of the bilayer film may be thermo-laminated to different types of substrates (e.g., paper, wood, etc.) to form polypropylene-EVA laminates.

One challenge to the utility of polypropylene-EVA laminates is achieving sufficient bond strength between the polypropylene film and the EVA layer. In order to improve the bonding between these layers, a tie layer may be placed between the polypropylene film and the EVA layer. However, adding a tie layer increases the cost associated with producing such materials and may detrimentally affect one of more physical properties (e.g., low haze, high gloss) of the material. Thus an ongoing need exists for novel laminate compositions having desirable physical and/or mechanical properties.

SUMMARY

Disclosed herein is a method including forming a bilayer polymer film having an oriented polypropylene film and a metallocene-catalyzed polypropylene film wherein the metallocene-catalyzed polypropylene film has a seal initiation temperature of from 80° C. to 130° C. The bilayer polymer film may have of an oriented polypropylene film and a metallocene-catalyzed polypropylene film. The metallocene-catalyzed polypropylene film may have a thickness of from 0.1 mil to 20 mil. The oriented polypropylene film may include uniaxially oriented polypropylene film, biaxially oriented polypropylene film, or combinations thereof. The oriented polypropylene film may be corona treated. The oriented polypropylene film may have a thickness of from 0.1 mil to 20 mil. The bilayer polymer film may have an adhesive strength of from 0.1 lbf to 10 lbf. The bilayer polymer film may have a gloss 45° of from 60 to 99. The bilayer polymer film may have a haze percentage of from 0.5% to 10%. The bilayer polymer film may have a thickness of from 0.2 mil to 20 mil. The forming of the bilayer polymer film may occur at a temperature of from 420° F. to 530° F. The forming of the bilayer polymer film may occur by extrusion coating the metallocene-catalyzed polypropylene film onto the biaxially oriented polypropylene film. The method may further include thermolaminating the bilayer polymer film with a substrate to form a laminate wherein the metallocene-catalyzed polypropylene film is disposed between the biaxially oriented polypropylene film and the substrate. The substrate may include paper, plastic, metal, wood, fabric, glass or combinations thereof. The laminate may be substantially free of ethylene-vinyl-acetate. The oriented polypropylene film may be subjected to a surface modification process. An article as produced by any of the previously disclosed methods.

Also disclosed herein is a laminate including a biaxially oriented polypropylene film, a metallocene-catalyzed polypropylene film, and a substrate wherein the metallocene-catalyzed polypropylene film is disposed between the biaxially oriented polypropylene film and the substrate. The metallocene-catalyzed polypropylene film may have a seal initiation temperature of from 80° C. to 130° C. The laminate may be substantially free of ethylene-vinyl-acetate.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

FIG. 1 is a schematic diagram of an extrusion coating apparatus.

FIGS. 2A and 2B illustrate a 180° peel force test.

FIG. 3 is a plot of force as a function of extension for the 180° peel test results for Sample 1 from Example 1.

FIG. 4 is a plot of force as a function of extension for the 180° peel test results for Sample 2 from Example 2.

FIG. 5 is a plot of force as a function of extension for the 180° peel test results for Sample 3 from Example 3.

FIG. 6 is a plot of force as a function of extension for the 180° peel test results for Sample 4 from Example 4.

FIG. 7 is a plot of average force as a function of extension for the 180° peel test results for Samples 1-4 from Examples 1-4.

FIGS. 8-11 are plots of force as a function of extension for the 180° peel test results for Samples 9-12 from Example 7.

FIG. 12 is a plot of average force as a function of extension for the 180° peel test results for Samples 9-12 from Example 7.

FIG. 13 is a plot of average force as a function of extension for the 180° peel test results for Sample 2, 11, and 12 from Examples 2 and 7.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

As used herein oriented polypropylene is designated “oPP;” metallocene-catalyzed polypropylene is designated “mPP;” bilayer polymer film is designated “BPF;” biaxially oriented polypropylene is designate “BOPP;” high crystallinity polypropylene is designated “HCPP;” polypropylene heterophasic copolymers are designated “PPHC;” ethylene propylene rubber is designated “EPR;” melt flow rate is designated “MFR;” metallocene-catalyzed random ethylene propylene copolymer is designated “mREPC;” seal initiation temperature is designated “SIT;” percentage xylene solubles is designated “XS %;” and ethylene vinyl acetate is designated “EVA.”

Disclosed herein are multilayer polymer films and methods of making and using same.

The multilayer polymer films include at least one oriented polypropylene (oPP) film layer and at least one metallocene-catalyzed polypropylene (mPP) film layer. In an embodiment, the multilayer film includes greater than 2 layers, alternatively 3, 4, 5, or 6 layers. Alternatively, the multilayer film includes 2 layers. Hereinafter, for simplicity, the discussion will refer to bilayer polymer films although it is to be understood that polymer films having greater than two layers are also contemplated.

In an embodiment, a bilayer polymer film (BPF) may have an oriented polypropylene (oPP) film layer and a metallocene-catalyzed polypropylene (mPP) film layer.

In an embodiment, the BPF includes an oriented polypropylene film layer. The polypropylene may be a homopolymer, a high crystallinity polypropylene, a polypropylene heterophasic copolymer, or combinations (e.g., blends) thereof. The polypropylene may be formed into a film and oriented to produce an oriented polypropylene film layer as described in more detail herein.

The polypropylene may be a homopolymer provided however that the homopolymer may contain up to 5% of another alpha-olefin, including but not limited to C₂-C₈ alpha-olefins such as ethylene and 1-butene. Despite the potential presence of small amounts of other alpha-olefins, the polypropylene is generally referred to as a polypropylene homopolymer (or substantially a homopolymer). Polypropylene homopolymers suitable for use in this disclosure may include any type of polypropylene known in the art with the aid of this disclosure. For example, the polypropylene homopolymer may be, isotactic polypropylene, hemi-isotactic, or combinations thereof. A polymer is “isotactic” when all of its pendant groups are arranged on the same side of the chain. In hemi-isotactic polymer, every other repeat unit has a random substituent.

A polypropylene suitable for use in this disclosure may be characterized by a number average molecular weight Mn of from 3.3×10⁴ Daltons to 8.3×10⁴ Daltons, alternatively from 4.1×10⁴ Daltons to 7.5×10⁴ Daltons, alternatively from 5.0×10⁴ Daltons to 6.6×10⁴ Daltons; a weight average molecular weight of from 3.0×10⁵ Daltons to 6.2×10⁵ Daltons, alternatively from 3.5×10⁵ Daltons to 5.7×10⁵ Daltons, alternatively from 4.0×10⁵ Daltons to 5.1×10⁵ Daltons; a polydispersity index of from 4.9 to 11.0, alternatively from 6.0 to 10.0, alternatively from 7.0 to 9.0; and a z-average molecular weight of from 9.7×10⁵ Daltons to 3.2×10⁶ Daltons, alternatively from 1.3×10⁶ Daltons to 2.8×10⁶ Daltons, alternatively from 1.7×10⁶ Daltons to 2.5×10⁶ Daltons. Specifically, for a polymeric composition the number-average molecular weight M_(n) is given by equation 1: M _(n) =ΣN _(x) M _(x)  (1) where N_(x) is the mole-fraction (or the number-fraction) of molecules whose weight is M_(x) The weight-average molecular weight M_(w) is given by equation 2: M _(w) =Σw _(x) M _(x)  (2) where w_(x) is the weight-fraction of molecules whose weight is M_(x). The polydispersity index (PDI) is given by equation 3: PDI=M _(w) /M _(n)  (3) The z-average molecular weight (M_(z)) is given by equation 4: M _(z) =Σw _(x) M _(x) ² /Σw _(x) M _(x)  (4) where w_(x) is the weight-fraction of molecules whose weight is M_(x).

In an embodiment, a polypropylene suitable for use in this disclosure may have a density of from 0.895 g/cc to 0.920 g/cc, alternatively from 0.900 g/cc to 0.915 g/cc, and alternatively from 0.905 g/cc to 0.915 g/cc as determined in accordance with ASTM D1505; a melting temperature of from 150° C. to 170° C., alternatively from 155° C. to 168° C., and alternatively from 160° C. to 165° C. as determined by differential scanning calorimetry; a melt flow rate of from 0.5 g/10 min. to 30 g/10 min., alternatively from 1.0 g/10 min. to 15 g/10 min., and alternatively from 1.5 g/10 min. to 5.0 g/10 min. as determined in accordance with ASTM D1238 condition “L”; a tensile modulus of from 200,000 psi to 350,000 psi; alternatively from 220,000 psi to 320,000 psi, and alternatively from 250,000 psi to 320,000 psi as determined in accordance with ASTM D638; a tensile stress at yield of from 3,000 psi to 6,000 psi, alternatively from 3,500 psi to 5,500 psi, and alternatively from 4,000 psi to 5,500 psi as determined in accordance with ASTM D638; a tensile strain at yield of from 5% to 30%, alternatively from 5% to 20%, and alternatively from 5% to 15% as determined in accordance with ASTM D638; a flexural modulus of from 120,000 psi to 330,000 psi, alternatively from 190,000 psi to 310,000 psi, and alternatively of from 220,000 psi to 300,000 psi as determined in accordance with ASTM D790; a Gardner impact of from 3 in-lb to 50 in-lb, alternatively from 5 in-lb to 30 in-lb, and alternatively from 9 in-lb to 25 in-lb as determined in accordance with ASTM D2463; a Notched Izod Impact Strength of from 0.2 ft lb/in to 20 ft lb/in, alternatively from 0.5 ft lb/in to 15 ft lb/in, and alternatively from 0.5 ft lb/in to 10 ft lb/in as determined in accordance with ASTM D256A; a hardness shore D of from 30 to 90, alternatively from 50 to 85, and alternatively from 60 to 80 as determined in accordance with ASTM D2240; and a heat distortion temperature of from 50° C. to 125° C., alternatively from 80° C. to 115° C., and alternatively from 90° C. to 110° C. as determined in accordance with ASTM D648.

Examples of polypropylene homopolymers suitable for use in this disclosure include without limitation grades 3371, 3271, 3270, 3276, and 3377, which are polypropylene homopolymers commercially available from Total Petrochemicals USA, Inc. In an embodiment, the polypropylene homopolymer (e.g., grade 3377) has generally the physical properties set forth in Table 1.

TABLE 1 Properties Typical Value Test Method Resin properties Density, g/cc 0.905 ASTM D1505 Melt Flow Rate (MFR), g/10 min. 3.5 ASTM D1238 condition “L” Melting Point, ° F. 325 DSC Film Properties, Oriented Haze, % 1 ASTM D1003 Gloss 45° 90 ASTM D 2457 Ultimate tensile MD, psi 19,000 ASTM D 882 Ultimate tensile TD, psi 38,000 ASTM D 882 Tensile modulus, MD, psi 350,000 ASTM D 882 Tensile modulus, TD, psi 600,000 ASTM D 882 Elongation MD, % 130 ASTM D 882 Elongation TD, % 50 ASTM D 882 WVTR, g/100 in 2/24 h/mil 0.3 ASTM F-1249-90 at 100° F., 90% RH

In another embodiment, the polypropylene may be a high crystallinity polypropylene homopolymer (HCPP). The HCPP may contain primarily isotactic polypropylene. The isotacticity in polymers may be measured via ¹³C NMR spectroscopy using meso pentads and can be expressed as percentage of meso pentads (% mmmm). As used herein, the term “meso pentads” refers to successive methyl groups located on the same side of the polymer chain. In an embodiment, the HCPP has a meso pentads percentage of greater than 97%, or greater than 98%, or greater than 99%. The HCPP may have some amount of atactic or amorphous polymer. The atactic portion of the polymer is soluble in xylene, and is thus termed the xylene soluble fraction (XS %). In determining XS %, the polymer is dissolved in boiling xylene and then the solution cooled to 0° C. that results in the precipitation of the isotactic or crystalline portion of the polymer. The XS % is that portion of the original amount that remained soluble in the cold xylene. Consequently, the XS % in the polymer is indicative of the extent of crystalline polymer formed. The total amount of polymer (100%) is the sum of the xylene soluble fraction and the xylene insoluble fraction, as determined in accordance with ASTM D5492-98. In an embodiment, the HCPP has a xylene soluble fraction of less than 1.5%, or less than 1.0%, or less than 0.5%.

In an embodiment, an HCPP suitable for use in this disclosure may have a density of from 0.895 g/cc to 0.920 g/cc, alternatively from 0.900 g/cc to 0.915 g/cc, and alternatively from 0.905 g/cc to 0.915 g/cc as determined in accordance with ASTM D1505; a melt flow rate of from 0.5 g/10 min. to 30 g/10 min., alternatively from 1.0 g/10 min. to 15 g/10 min., and alternatively from 1.5 g/10 min. to 5.0 g/10 min. as determined in accordance with ASTM D1238; a secant modulus in the machine direction (MD) of from 350,000 psi to 420,000 psi; alternatively from 380,000 psi to 420,000 psi, and alternatively from 400,000 psi to 420,000 psi as determined in accordance with ASTM D882; a secant modulus in the transverse direction (TD) of from 400,000 psi to 700,000 psi, alternatively from 500,000 psi to 700,000 psi, and alternatively from 600,000 psi to 700,000 psi as determined in accordance with ASTM D882; a tensile strength at break in the MD of from 19,000 psi to 28,000 psi, alternatively from 22,000 psi to 28,000 psi, and alternatively from 25,000 psi to 28,000 psi as determined in accordance with ASTM D882; a tensile strength at break in the TD of from 20,000 psi to 40,000 psi, alternatively from 30,000 psi to 40,000 psi, and alternatively of from 35,000 psi to 40,000 psi as determined in accordance with ASTM D882; an elongation at break in the MD from 50% to 200%, alternatively from 100% to 180%, and alternatively from 120% to 150% as determined in accordance with ASTM D882; an elongation at break in the TD of from 50% to 150%, alternatively from 60% to 100%, and alternatively from 80% to 100% as determined in accordance with ASTM D882; a melting temperature of from 150° C. to 170° C., alternatively from 155° C. to 170° C., and alternatively from 160° C. to 170° C. as determined by differential scanning calorimetry; a gloss at 45° of from 70 to 95, alternatively from 75 to 90, and alternatively from 80 to 90 as determined in accordance with ASTM D2457; a percentage haze of from 0.5% to 2.0%, alternatively from 0.5% to 1.5%, and alternatively from 0.5% to 1.0% as determined in accordance with ASTM D1003; and a water vapor transmission rate of from 0.15 to 0.30 g-mil/100 in²/day, alternatively from 0.15 to 0.25 g-mil/100 in²/day, and alternatively from 0.20 to 0.21 g-mil/100 in²/day as determined in accordance with ASTM F1249-90.

An example of an HCPP suitable for use in this disclosure includes without limitation grade 3270, which is an HCPP commercially available from Total Petrochemicals USA, Inc. The HCPP (e.g., grade 3270) may generally have the physical properties set forth in Table 2.

TABLE 2 Properties Typical Value Test Method Physical Density, g/cc 0.910 ASTM D1505 Melt Mass-Flow Rate (MFR) 2.0 ASTM D1238 (230° C./2.16 kg), g/10 min. BOPP Mechanical Secant Modulus MD, psi 420,000 ASTM 882 Secant Modulus TD, psi 700,000 ASTM 882 Tensile Strength at Break MD, psi 28,000 ASTM 882 Tensile Strength at Break TD, psi 39,000 ASTM 882 Elongation at Break MD, % 150 ASTM 882 Elongation at Break TD, % 60 ASTM 882 Thermal Melting Temperature, ° F. 329 DSC Optical Gloss (45°) 85 ASTM D2457 Haze, % 1.0 ASTM D1003 Barrier Water Vapor Transmission, 0.2 ASTM F1249- 100° F., 90% R.H, g-mil/100 in²/day 90

In another embodiment, the polypropylene may be a polypropylene heterophasic copolymer (PPHC) wherein a polypropylene homopolymer phase or component is joined to a copolymer phase or component. The PPHC may have from greater than 6.5% to less than 11.5% by weight ethylene, alternatively from 8.5% to less than 10.5%, alternatively from 9.5% ethylene based on the total weight of the PPHC. Herein, percentages of a component refer to the percent by weight of that component in the total composition unless otherwise noted.

The copolymer phase of a PPHC may be a random copolymer of propylene and ethylene, also referred to as an ethylene/propylene rubber (EPR). PP impact copolymers show distinct homopolymer phases that are interrupted by short sequences or blocks having a random arrangement of ethylene and propylene. In comparison to random copolymers, the block segments comprising the EPR may have certain polymeric characteristics (e.g., intrinsic viscosity) that differ from that of the copolymer as a whole. In an embodiment, the EPR portion of the PPHC includes greater than 14 wt. % of the PPHC, alternatively greater than 18 wt. % of the PPHC, alternatively from 14 wt. % to 18 wt. % of the PPHC.

The amount of ethylene present in the EPR portion of the PPHC may be from 38 wt. % to 50 wt. %, alternatively from 40 wt. % to 45 wt, % based on the total weight of the EPR portion. The amount of ethylene present in the EPR portion of the PPHC may be determined spectrophotometrically using a Fourier transform infrared spectroscopy (FTIR) method. Specifically, the FTIR spectrum of a polymeric sample is recorded for a series of samples having a known EPR ethylene content. The ratio of transmittance at 720 cm⁻¹/900 cm⁻¹ is calculated for each ethylene concentration and a calibration curve may then be constructed. Linear regression analysis on the calibration curve can then be carried out to derive an equation that is then used to determine the EPR ethylene content for a sample material.

The EPR portion of the PPHC may exhibit an intrinsic viscosity different from that of the propylene homopolymer component. Herein intrinsic viscosity refers to the capability of a polymer in solution to increase the viscosity of said solution. Viscosity is defined herein as the resistance to flow due to internal friction. In an embodiment, the intrinsic viscosity of the EPR portion of the PPHC may be greater than 2.0 dl/g, alternatively from 2.0 dl/g to 3.0 dl/g, alternatively from 2.4 dl/g to 3.0 dl/g, alternatively from 2.4 dl/g to 2.7 dl/g, alternatively from 2.6 dl/g to 2.8 dl/g. The intrinsic viscosity of the EPR portion of the PPHC is determined in accordance with ASTM D5225.

In an embodiment, the PPHC may have a melt flow rate (MFR) of from 65 g/10 min. to 130 g/10 min., alternatively from 70 g/10 min. to 120 g/10 min., alternatively from 70 g/10 min. to 100 g/10 min., alternatively from 70 g/10 min. to 90 g/10 min., alternatively from 75 g/10 min. to 85 g/10 min., alternatively 90 g/10 min. Excellent flow properties as indicated by a high MFR allow for high throughput manufacturing of molded polymeric components. In an embodiment, the PPHC is a reactor grade resin without modification, which may also be termed a low order PP. In some embodiments, the PPHC is a controlled rheology grade resin, wherein the melt flow rate has been adjusted by various techniques such as visbreaking. For example, MFR may be increased by visbreaking as described in U.S. Pat. No. 6,503,990, which is incorporated by reference in its entirety. As described in that publication, quantities of peroxide are mixed with polymer resin in flake, powder, or pellet form to increase the MFR of the resin. MFR as defined herein refers to the quantity of a melted polymer resin that will flow through an orifice at a specified temperature and under a specified load. The MFR may be determined using a dead-weight piston Plastometer that extrudes polypropylene through an orifice of specified dimensions at a temperature of 230° C. and a load of 2.16 kg in accordance with ASTM D1238.

Representative examples of suitable PPHCs include without limitation grades 4920W and 4920WZ, which are impact copolymer resins commercially available from Total Petrochemicals USA Inc. In an embodiment, the PPHC (e.g., grade 4920W) has generally the physical properties set forth in Table 3.

TABLE 3 Properties Typical Value ASTM Method Physical Melt Flow, g/10 min. 100 D1238 Density, g/cc 0.905 D1505 Melting Point, ° C. 160-165 DSC Mechanical Tensile strength at Yield, psi (MPa) 3700 (25) D638 Elongation at Yield, % 6 D638 Flexural Modulus, psi (MPa) 190,000 (1,300) D790 Notched-ft. lb./in. (J/m)  1.0 (50) ASTM D256A Thermal Heat Deflection, ° C. 90 D648

In an embodiment, the polypropylene may also contain additives to impart desired physical properties, such as printability, increased gloss, or a reduced blocking tendency. Examples of additives include without limitation stabilizers, ultra-violet screening agents, oxidants, anti-oxidants, anti-static agents, ultraviolet light absorbents, fire retardants, processing oils, mold release agents, coloring agents, pigments/dyes, fillers, and/or other additives known to one skilled in the art. The aforementioned additives may be used either singularly or in combination to form various formulations of the polymer. For example, stabilizers or stabilization agents may be employed to help protect the polymer resin from degradation due to exposure to excessive temperatures and/or ultraviolet light. These additives may be included in amounts effective to impart the desired properties. Effective additive amounts and processes for inclusion of these additives to polymeric compositions may be determined by one skilled in the art with the aid of this disclosure.

The polypropylene for oPP film may be prepared using any suitable catalyst known to one or ordinary skill in the art. For example, the polypropylene may be prepared using a Ziegler-Natta catalyst.

In an embodiment, the polypropylene is prepared using Ziegler-Natta catalysts, which are typically based on titanium and organometallic aluminum compounds, for example triethylaluminum (C₂H₅)₃Al. Ziegler-Natta catalysts and processes for forming such catalysts are known in the art and examples of such are described in U.S. Pat. Nos. 4,298,718; 4,544,717; and 4,767,735, each of which is incorporated by reference herein.

The polypropylene may be formed by placing propylene alone in a suitable reaction vessel in the presence of a catalyst (e.g., Ziegler-Natta) and under suitable reaction conditions for polymerization thereof. Standard equipment and processes for polymerizing the propylene into a polymer are known to one skilled in the art. Such processes may include solution phase, gas phase, slurry phase, bulk phase, high pressure processes or combinations thereof. Such processes are described in detail in U.S. Pat. Nos. 5,525,678; 6,420,580; 6,380,328; 6,359,072; 6,346,586; 6,340,730; 6,339,134; 6,300,436; 6,274,684; 6,271,323; 6,248,845; 6,245,868; 6,245,705; 6,242,545; 6,211,105; 6,207,606; 6,180,735; and 6,147,173, which are incorporated herein by reference in their entirety.

In an embodiment, the polypropylene is formed by a gas phase polymerization process. One example of a gas phase polymerization process includes a continuous cycle system, wherein a cycling gas stream (otherwise known as a recycle stream or fluidizing medium) is heated in a reactor by heat of polymerization. The heat is removed from the cycling gas stream in another part of the cycle by a cooling system external to the reactor. The cycling gas stream containing one or more monomers may be continuously cycled through a fluidized bed in the presence of a catalyst under reactive conditions. The cycling gas stream is generally withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product may be withdrawn from the reactor and fresh monomer may be added to replace the polymerized monomer. The reactor pressure in a gas phase process may vary from about 100 psig to about 500 psig, or from about 200 psig to about 400 psig, or from about 250 psig to about 350 psig. The reactor temperature in a gas phase process may vary from about 30° C. to about 120° C., or from about 60° C. to about 115° C., or from about 70° C. to about 110° C., or from about 70° C. to about 95° C., for example U.S. Pat. Nos. 4,543,399; 4,588,790; 5,028,670; 5,317,036; 5,352,749; 5,405,922; 5,436,304; 5,456,471; 5,462,999; 5,616,661; 5,627,242; 5,665,818; 5,677,375; and 5,668,228, which are incorporated herein by reference in their entirety.

In an embodiment, the polypropylene is formed by a slurry phase polymerization process. Slurry phase processes generally include forming a suspension of solid, particulate polymer in a liquid polymerization medium, to which monomers and optionally hydrogen, along with catalyst, are added. The suspension (which may include diluents) may be intermittently or continuously removed from the reactor where the volatile components can be separated from the polymer and recycled, optionally after a distillation, to the reactor. The liquefied diluent employed in the polymerization medium may include a C₃ to C₇ alkane (e.g., hexane or isobutene). The medium employed is generally liquid under the conditions of polymerization and relatively inert. A bulk phase process is similar to that of a slurry process. However, a process may be a bulk process, a slurry process or a bulk slurry process.

In an embodiment, the BPF includes metallocene-catalyzed polypropylene (mPP) film layer (i.e., a film layer comprising polypropylene produced using a metallocene catalyst). The mPP may be a homopolymer or a copolymer, for example a copolymer of propylene with one or more alpha olefin monomers such as ethylene, butene, hexene, etc. In an embodiment, the mPP film includes a metallocene-catalyzed random ethylene-propylene (C₂/C₃) copolymer (mREPC) and may include of from 2 wt. % to 10 wt. % ethylene, alternatively from 3 wt. % to 9 wt. % ethylene, alternatively from 4 wt. % to 8 wt. % ethylene. The mPP film layer may have a seal initiation temperature (SIT) of from 80° C. to 130° C., alternatively from 95° C. to 125° C., alternatively from 90° C. to 120° C. Herein the SIT refers to the minimum sealing temperature required to form a seal of significant strength, which varies depending on the applications. Further, a mPP suitable for use in this disclosure may be characterized by a number average molecular weight Mn of from 5.1×10⁴ to 9.3×10⁴, alternatively from 5.8×10⁴ to 8.6×10⁴, alternatively from 6.5×10⁴ to 7.9×10⁴; a weight average molecular weight of from 1.67×10⁵ to 2.20×10⁵, alternatively from 1.75×10⁵ to 2.11×10⁵, alternatively from 1.84×10⁵ to 2.02×10⁵; a polydispersity index of from 2.1 to 3.3, alternatively from 2.3 to 3.1, alternatively from 2.5 to 2.9; and a z-average molecular weight of from 2.98×10⁵ to 4.22×10⁵, alternatively from 3.19×10⁵ to 4.01×10⁵, alternatively from 3.40×10⁵ to 3.81×10⁵.

In ethylene-propylene random copolymers, the ethylene molecules are inserted randomly into the polymer backbone between repeating propylene molecules, hence the term random copolymer. In the preparation of a mREPC a certain amount of amorphous polymer is produced. This amorphous or atactic polymer is soluble in xylene and is thus termed the xylene soluble fraction or percent xylene solubles (XS %). In determining XS %, the polymer is dissolved in hot xylene and then the solution is cooled to 0° C. which results in the precipitation of the isotactic or crystalline portion of the polymer. The XS % is that portion of the original amount that remained soluble in the cold xylene. Consequently, the XS % in the polymer is further indicative of the extent of crystalline polymer formed. In an embodiment, the mREPC has a xylene soluble fraction of from 0.1% to 6.0%; alternatively from 0.2% to 2.0%; and alternatively from 0.3% to 1.0%, as determined in accordance with ASTM D 5492-98.

In an embodiment, an mREPC suitable for use in this disclosure may have a density of from 0.890 g/cc to 0.920 g/cc, alternatively from 0.895 g/cc to 0.915 g/cc, and alternatively from 0.900 g/cc to 0.910 g/cc as determined in accordance with ASTM D-1505. In an embodiment, an mREPC suitable for use in this disclosure may have a melt flow rate of from 0.5 g/10 min. to 2000 g/10 min., alternatively from 1 g/10 min. to 1000 g/10 min., and alternatively from 10 g/10 min. to 500 g/10 min., as determined in accordance with ASTM D-1238 condition “L.” In an embodiment, a film prepared from an mREPC suitable for use in this disclosure may have a gloss at 45° of from 70 to 95, alternatively from 75 to 90, and alternatively from 80 to 90 as determined in accordance with ASTM D-2457.

An example of a suitable mREPC suitable for use in this disclosure includes without limitation a metallocene catalyzed ethylene-propylene random copolymer known as grade EOD 02-15 available from Total Petrochemicals USA, Inc. In an embodiment, the mREPC (e.g., grade EOD 02-15) generally has the physical properties set forth in Table 4.

TABLE 4 Resin Properties Typical Value ASTM Method Melt Flow, g/10 min. 11 D 1238 Density, g/cc 0.895 D 1505 Melting Point, ° F. (° C.)   246 (119) DSC ⁽¹⁾ Film Properties ⁽¹⁾ Non-oriented- 2 mil (50 μm) Haze, % 0.3 D 1003 Gloss @ 45°, % 90 D 2457 1% Secant Modulus (MD), psi (MPa) 50,000 (345) D 882 Ultimate Tensile Strength (MD), 5,000 (35) D 882 psi (MPa) Ultimate Elongation (MD), % 700 D 882 Heat Seal Temperature ⁽²⁾, ° F. (° C.)   221 (105) ⁽¹⁾ MP determined with a DSC-2 Differential Scanning Calorimeter. ⁽²⁾ Seal condition: die pressure 60 psi (413 kPa), dwell time 1.0 sec

mPP homopolymers may be formed by placing propylene in a suitable reaction vessel in the presence of a metallocene catalyst and/or optionally additives and under suitable reaction conditions for polymerization thereof.

mPP copolymers (i.e., mREPC) may be formed by placing propylene in combination with a co-monomer (e.g., ethylene) in a suitable reaction vessel in the presence of a metallocene catalyst and/or optionally additives and under suitable reaction conditions for polymerization thereof. Preparation of mPPs (i.e., mREPCs) are described in further detail in U.S. Pat. Nos. 5,158,920, 5,416,228, 5,789,502, 5,807,800, 5,968,864, 6,225,251, and 6,432,860, each of which is incorporated herein by reference in its entirety.

In an embodiment, a method of preparing a BPF includes preparing an oPP film and contacting an mPP film with the oPP film to form a multi-layer film (e.g., a bilayer film). In such an embodiment, the oPP film may be prepared by first melting the polypropylene in an extruder. Next, the molten polypropylene is extruded through a slot or a die to form a thin extruded polypropylene film. The extruded polypropylene film is then adhered to a cooled surface, such as a chill roll that may be in contact with a water bath. The chill roll functions to immediately quench the film. The polypropylene film may then be passed through rollers designed to stretch the film in one direction to produce a uniaxially oriented polypropylene film, alternatively in differing axial directions to produce biaxially oriented polypropylene (i.e., BOPP) films. The uniaxially or biaxially oriented film (collectively referred to herein as oPP film) may be further trimmed and rolled for transport or storage. In an embodiment, the oPP film has a thickness of from 0.1 mil to 20 mil, alternatively from 0.25 mil to 20 mil, alternatively from 0.30 mil to 20 mil.

In some embodiments, the oPP film may be subjected to a surface modification process designed to increase the surface tension of the film. Examples of surface modification processes include without limitation corona treatment, flame treatment and plasma treatment. Corona treatment is an electrical process that uses ionized air to increase the surface tension of nonporous substrates. Flame treatment is a process of burning away surface contaminants by forcibly spraying a flame onto a substrate. Plasma treatment is a process of creating plasma in an inert gas to increase surface energy and wetting ability of a substrate. In an embodiment, the oPP film of this disclosure is subjected to corona treatment following extrusion. Methods and conditions for corona treatment of an oPP film are known to one of ordinary skill in the art with the aid of this disclosure.

Examples of suitable oPP films include without limitation TAPEFILM TH20 and TAPEFILM TH30 which are oPP tape films commercially available from OppFilm Fallsington, Pa. In an embodiment, the oPP films (e.g., TAPEFILM TH20, TAPEFILM TH30) have generally the physical properties set forth in Table 5.

TABLE 5 Typical Value Properties TAPEFILM TH20 TAPEFILM TH30 ASTM Method Haze, % 1.0 D 1003 Gloss at 45° 90 D 2457 Dynamic C.O.F (Film/film) 03 D 1894 Tensile strength MD, N/mm² 150 D 882 Tensile strength TD, N/mm² 300 D 882 Elongation at break MD, % 130 D 882 Elongation at break TD, % 50 D 882 Modulus MD, N/mm² 2000 D 882 Modulus TD, N/mm² 2800 D 882 Wet tension (corona treatment), dinas, cm 38 2578 Water vapor transmission 38°, 90% HR 5.6 4.7 F 1249 Oxygen transmission at 22° C., 0% HR 1800 1600 D 1434

After the oPP film is prepared, the method of preparing a BPF may further include extrusion coating an mPP layer onto the oPP film layer. FIG. 1 is a schematic diagram of an extrusion coating apparatus 100 for use in the process of preparing a BPF. Referring to FIG. 1, the process may be carried out by providing an oPP, which is usually in the form of a rolled oPP film 110. The rolled oPP film 110 is unwound using an unwinder 105 where an unrolled oPP film 115 is guided using guide rollers 120 and 125 toward a nip roller 130. Next, an mPP 140 is melted and extruded through a die 135 at a temperature of from 420° F. to 530° F., alternatively from 440° F. to 520° F., alternatively from 490° F. to 510° F. The extruded mPP 140 is then laid onto (i.e., contacted with) the unrolled oPP film 115 at a nip 150. Contacting of the mPP 140 and the oPP film 110 at nip 150 at adequate pressure causes the mPP 140 to adhere to the oPP film 115 to form a BPF 155. In an embodiment, the apparatus is configured such that the pressure applied may be adjusted to meet a process-desired need. The BPF 155 is then passed onto a cooling cylinder such as a chilled roll 145, and guided with guide roller 160 towards rollers 165. From rollers 165, the BPF 155 is wound using winder 170 and collected as a rolled BPF film 175.

The oPP film layer may have a thickness of from 0.1 mil to 20 mil, alternatively from 0.25 mil to 20 mil, alternatively from 0.3 mil to 20 mil. The mPP film layer may have a thickness of from 0.1 mil to 20 mil, alternatively from 0.25 mil to 20 mil, alternatively from 0.3 mil to 20 mil. In such embodiments, the resultant BPF having an oPP film layer and a mPP film layer has a thickness of from 0.2 mil to 20 mil, alternatively from 0.25 mil to 20 mil, alternatively from 0.3 mil to 20 mil.

In an embodiment, a BPF of the type described herein may include an oPP, an mPP and a tie layer. Alternatively the BPF does not include a tie layer. Tie layers are adhesive layers that are typically added to improve the adhesion between two materials.

The BPF comprising an mPP film layer and an oPP film layer of the type described herein may have display a number of desirable physical and/or optical properties. In an embodiment, the BPFs of the type described herein have a haze percentage of from 0.5% to 10%, or from 1% to 9%, or from 1.5% to 7%. Haze is the cloudy appearance of a material caused by light scattered from within the material or from its surface. The haze of a material can be determined in accordance with ASTM D1003-00 for a haze percentage of equal to or lower than 30%. A material having a haze percentage of greater than 30% can be determined in accordance with ASTM E167.

In an embodiment, BPFs of the type described herein may have a gloss 45° of from 60 to 99, or from 61 to 98, or from 62 to 95. The gloss of a material is based on the interaction of light with the surface of a material, more specifically the ability of the surface to reflect light in a specular direction. Gloss is measured by measuring the degree of gloss as a function of the angle of the incident light, for example at 45° incident angle (also known as “gloss 45°”), and may be determined in accordance with ASTM D2457.

In an embodiment, a BPF of the type described herein may be used in thermo-lamination applications to form laminates. In such an embodiment, the BPF may be applied to a substrate, wherein the mPP film layer is disposed between the oPP film layer and the substrate, and then heated to form a laminate. The substrate may include any suitable substrate such as paper, plastic, metal, wood, fabric, glass, or combinations thereof. In thermo-lamination applications, the mPP film layer of the BPF may function as a heat seal layer.

In an embodiment, a laminate is formed which has a substrate, an mPP film layer and an oPP film layer of the type described herein. In an embodiment, the laminate includes less than 1 wt. % EVA, alternatively less than 0.5, 0.1, 0.01, 0.001 or 0.001 wt. % EVA. Alternatively, the laminate is substantially free of EVA.

The laminate including a BPF having an mPP film layer and an oPP film layer of the type described herein may display desirable mechanical properties. In an embodiment, the laminate may exhibit an adhesive strength of from 0.1 lb_(f) to 10 lb_(f) alternatively from 0.25 lb_(f) to 9 lb_(f), alternatively from 0.5 lb_(f) to 7 lb_(f) based on a 180° peel strength test.

FIGS. 2A and 2B illustrate a 180° peel strength test 200. Referring to FIG. 2A, the test 200 is carried out by contacting a BPF 205 comprising an oPP film layer 210 and an mPP film layer 215 with a substrate such as a bond paper 220 wherein the mPP film layer 215 of the BPF 205 is facing the bond paper 220. Next, two heated bars 225 are pressed (arrows 230) onto the BPF 205 and the bond paper 220 at a temperature of 90° C. for one second. Referring now to FIG. 2B, the heated bars 225 are then removed (arrows 235) and a laminate 240 is formed. The laminate 240 is cooled for one minute. Next, the BPF 205 is peeled off from the bond paper 220 by applying two opposing forces 245. Any suitable tensile tester unit such as a 5500R Model 1122 commercially available from INSTRON may be used to conduct the peel strength experiment.

The BPFs of this disclosure may be converted to various end-use articles. Examples of end use articles into which the BPFs of this disclosure may be formed include laminates (for packaging, printed papers, etc.), laminate flooring compositions, polymeric foam substrate, decorative surfaces (e.g., crown molding, etc.), weatherable outdoor materials, point-of-purchase signs and displays, housewares and consumer goods, cosmetics packaging, outdoor replacement materials, lids and containers (i.e., for deli, fruit, candies and cookies), appliances, utensils, and the like.

EXAMPLES

The disclosure having been generally described, the following examples are given as particular embodiments of the disclosure and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner.

Example 1

The strength of adhesion for a BPF comprising an mPP film layer and a BOPP film layer produced at 440° F. was investigated. A BPF sample, designated Sample 1, was prepared. The BOPP film used was a corona treated BOPP film from OppFilm, Lima, Peru. The mPP used was EOD02-15, which is an mPP with an SIT of 105° C. available from Total Petrochemicals USA, Inc. No tie layer was used between the mPP and BOPP film.

The sample was produced by extrusion coating an mPP layer onto the BOPP film using a laboratory extruder as described previously with reference to FIG. 1. The details of processing parameters including temperatures, pressures, die gap, and screw speed for all samples are tabulated in Table 6. The thickness of the mPP film was adjusted by adjusting the line speed resulting in an mPP layer that was approximately 1 mil (25 μm) thick. The final BPF thickness was 2.0 mil (50 μm).

TABLE 6 Parameter Zone 1 temperature 370° F. Zone 2 temperature 400° F. Zone 3 temperature 415° F. Zone 4 temperature 440° F. Clamp ring temperature 440° F. Adaptor temperature 440° F. Feedblock temperature 440° F. Die temperature 440° F. Melt temperature 408° F. Melt pressure 290 psig Die gap 10 mil Screw speed 8 rpm Nip roll pressure 50 psig Chilled roll pressure 40 psig Film speed 20 ft/min

The adhesion strength of Sample 1 was determined by measuring the 180° peel force as discussed previously herein with reference to FIG. 2. The experiment was repeated six times. FIG. 3 shows the 180° peel force as a function of extension.

Example 2

The strength of adhesion between an mPP layer and a BOPP layer of a BPF produced at 500° F. was investigated. A bi-layer film sample, designated Sample 2, was prepared. The component materials and method of producing the bilayer film were described in Example 1. The details of processing parameters including temperatures, pressures, die gap, and screw speed for all samples are tabulated in Table 7. The thickness of the mPP film was adjusted by adjusting the line speed resulting in an mPP layer that was approximately 1 mil (25 μm) thick. The final BPF thickness was 2 mil.

TABLE 7 Parameter Samples 7-12 Zone 1 temperature 370° F. Zone 2 temperature 400° F. Zone 3 temperature 415° F. Zone 4 temperature 450° F. Clamp ring temperature 500° F. Adaptor temperature 510° F. Feedblock temperature 510° F. Die temperature 510° F. Melt temperature 427° F. Melt pressure 350 psig Die gap 10 mil Screw speed 12 rpm Nip roll pressure 50 psig Chilled roll pressure 40 psig Film speed 20 ft/min

The adhesive strength of Sample 2 was determined by measuring the 180° peel force and the experiment was repeated six times. FIG. 4 shows the 180° peel force as a function of extension.

The results demonstrated that the 180° peel forces were higher for Sample 2 when compared to Sample 1 from Example 1. The results suggest that EOD02-15 has a greater adhesive strength when coated at 500° F. instead of 440° F. as shown in Example 1.

Example 3

The strength of adhesion between an mPP and a BOPP of a BPF produced at 440° F. was investigated using an mPP having a lower SIT. A bi-layer film sample, designated Sample 3, was prepared. The BOPP used was that described in Example 1 and the mPP was EOD07-21, which is an mPP with a SIT of 98° C. available from Total Petrochemicals USA, Inc. The details of processing parameters including temperatures, pressures, die gap, and screw speed for Sample 3 are tabulated in Table 6. The thickness of the mPP film was adjusted by adjusting the line speed so resulting in an mPP layer that was approximately 1 mil (25 μm) thick. The final BPF thickness was 2.0 mil.

The adhesive strength of Sample 3 was determined by measuring the 180° peel force and the experiment was repeated five times. FIG. 5 shows the 180° peel force as a function of extension. The results demonstrated that the 180° peel forces were not higher for Sample 3 when compared to Sample 1 from Example 1.

Example 4

A bi-layer film sample, designated Sample 4, was prepared. The BOPP and the mPP used were similar to those used Example 3. The bilayer films (approximately 1 mil thick) were produced using procedures similar to those described in Example 1. The details of processing parameters including temperatures, pressures, die gap, and screw speed were similar to Example 2 which are tabulated in Table 7.

Sample 4 was tested for the adhesion by measuring the 180° peel force and the experiment was repeated 7 times. FIG. 6 shows the 180° peel force as a function of extension. The results demonstrate that the 180° peel forces were lower for Sample 4 when compared to Sample 2 from Example 2. The results were surprising since EOD07-21 has a lower SIT than EOD02-15. In addition, the increase in peel force trend observed by increasing the processing temperature from 440° F. to 500° F. as shown in Examples 1 and 2 was not observed for Examples 3 and 4.

Example 5

The haze and gloss of Samples 1-4 from Examples 1-4 were determined. The results are tabulated in Table 8.

TABLE 8 Sample 1 Sample 2 Sample 3 Sample 4 Haze % 6.3 6 5.4 1.8 Haze std. dev 0.18 0.16 0.19 0.95 Gloss 45° 79 64 68.8 83.3 Gloss 45° std. dev 4.4 5.6 6.4 3.2

The results demonstrated that significantly clear and glossy film structures can be produced with either EOD02-15 or EOD07-21.

Example 6

The average 180° peel force for Samples 1-4 from Examples 1-4 were determined. The results are shown in FIG. 7, which is a plot of average 180° peel force as a function of extension. Referring to FIG. 7, EOD02-15 extrusion coated at 500° F. (Sample 2) shows a higher average 180° peel force than the other samples, which suggests that EOD02-15 extrusion coated at 500° F. had higher adhesion strength to BOPP films.

Example 7

Films comprising a BOPP layer and an EVA coating with differing tie layers were prepared and the adhesion of the BOPP and EVA compared. Four films, designated Samples 5-8, were prepared using EOD05-07 as the base resin. EOD 05-07 is a polypropylene resin commercially available from Total Petrochemicals USA, Inc. Sample 5 included the BOPP film and a tie layer having a corona treated Basell 7432 resin. Basell 7432 is an ethylene-butylene-propylene terpolymer layer commercially available from Basell Service Co, The Netherlands. Sample 6 had the BOPP film and a tie layer including a corona treated HLDPE FH35 SC35 resin. HLDPE FH35 SC35 is a medium density polyethylene layer commercially available from Braskem, Brazil. Sample 7 had a corona treated BOPP film without a tie layer. Sample 8 had a BOPP film and a tie layer including a corona treated Basell 7416. Basell 7416 is an ethylene propylene copolymer layer, commercially available from Basell Service Co, The Netherlands. The thickness of the BOPP films was 0.0010 in. The surface tension of the corona-treated side of all samples was measured using AccuDyne Test Ink and the results are tabulated in Table 9.

TABLE 9 Sample Surface Tension (dyne/cm) 5 ~57 6 >69 7 >69 8 >69

Next, Samples 5-8 were extrusion coated with a 1 mil (−25 μm) thick EVA layer to form Samples 9-12 using a similar procedure described previously. The EVA was ELVAX 460 resin, which is a commercially available 18% vinyl acetate EVA resin from DuPont, North America. The details of processing parameters including temperatures, pressures, die gap, and screw speed for all samples are tabulated in Table 10.

TABLE 10 Parameter Samples 7-12 Zone 1 temperature 370° F. Zone 2 temperature 400° F. Zone 3 temperature 415° F. Zone 4 temperature 450° F. Clamp ring temperature 470° F. Adaptor temperature 470° F. Feedblock temperature 470° F. Die temperature 470° F. Melt temperature 428° F. Melt pressure ~1900 psig Die gap 10 mil Screw speed 23 rpm Nip roll pressure (L/R) 50/60 psig Take-off top roll temperature 55° F.

Paper separators were manually attached to the BOPP film at regular intervals upstream of the extrusion die during the coating process to provide separation points between the EVA coating and the BOPP film. The 180° peel tests were conducted on Samples 9-12 and were repeated between 5-8 times. The results for Samples 9-12 are shown in FIGS. 8-11 respectively. FIG. 12 shows the average 180° peel force as a function of extension for Samples 9-12.

The results demonstrate that EVA adheres strongly to the BOPP film comprising a corona treated ethylene propylene copolymer tie layer (Sample 12) and poorly to the corona treated BOPP homopolymer (Sample 11). The results further demonstrate that a mPP of the type described herein (e.g., EOD02-15) exhibits increased adhesion to a corona treated BOPP surface than an 18% EVA material. The clarity and low melting point of an MPP of the type described herein could prove highly beneficial for certain lamination applications. Furthermore, the simplicity of a bi-layer sealable material, when compare to a tri-layer EVA/RCP/BOPP material, may also beneficially impact the costs associated with the production of laminates.

While various embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the subject matter disclosed herein are possible and are within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R_(L), and an upper limit, R_(U), is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R_(L)+k*(R_(U)−R_(L)), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, etc.

Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present disclosure. Thus, the claims are a further description and are an addition to the embodiments of the present disclosure. The discussion of a reference is not an admission that it is prior art to the present disclosure, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein. 

What is claimed is:
 1. A method comprising: forming a bilayer polymer film comprising an oriented polypropylene film and a metallocene-catalyzed polypropylene film, wherein the metallocene-catalyzed polypropylene film has a seal initiation temperature of between 105° C. and 120° C., and wherein the metallocene-catalyzed polypropylene film comprises metallocene catalyzed ethylene-propylene random copolymer having melt flow rate of from 10 g/10 min. to 500 g/10 min, wherein the bilayer polymer film does not include a tie layer between the oriented polypropylene film and the metallocene-catalyzed polypropylene film, and wherein the bilayer polymer film has a haze percentage of from 1.5% to 7%.
 2. The method of claim 1 wherein the metallocene-catalyzed polypropylene film has a thickness of from 0.1 mil to 20 mil.
 3. The method of claim 1 wherein the oriented polypropylene film comprises uniaxially oriented polypropylene film, biaxially oriented polypropylene film, or combinations thereof.
 4. The method of claim 1 wherein the oriented polypropylene film is corona treated.
 5. The method of claim 1 wherein the oriented polypropylene film has a thickness of from 0.1 mil to 20 mil.
 6. The method of claim 1 wherein the bilayer polymer film has an adhesive strength of from 0.1 lbf to 10 lbf.
 7. The method of claim 1 wherein the bilayer polymer film has a gloss 45° of from 60 to
 99. 8. The method of claim 1 wherein the bilayer polymer film has a thickness of from 0.2 mil to 20 mil.
 9. The method of claim 1 wherein the forming of the bilayer polymer film occurs at a temperature of from 420° F. to 530° F.
 10. The method of claim 1 wherein the oriented polypropylene film comprises biaxially oriented polypropylene film, and wherein the forming of the bilayer polymer film occurs by extrusion coating the metallocene-catalyzed polypropylene film onto the biaxially oriented polypropylene film.
 11. The method of claim 1 further comprising: thermolaminating the bilayer polymer film with a substrate to form a laminate, wherein the metallocene-catalyzed polypropylene film is disposed between the oriented polypropylene film and the substrate.
 12. The method of claim 11 wherein the substrate comprises paper, plastic, metal, wood, fabric, glass or combinations thereof.
 13. The method of claim 11 wherein the laminate is substantially free of ethylene-vinyl-acetate.
 14. The method of claim 1 wherein the oriented polypropylene film is subjected to a surface modification process.
 15. The method of claim 1, wherein the metallocene-catalyzed polypropylene film is a non-oriented film.
 16. A method comprising: biaxially orienting a polypropylene film to prepare a biaxially oriented polypropylene film; and after preparing the biaxially oriented polypropylene film, extrusion coating a metallocene-catalyzed polypropylene film onto the biaxially oriented polypropylene film to form a bilayer polymer film; wherein the metallocene-catalyzed polypropylene film has a seal initiation temperature of between 105° C. and 120° C., wherein the metallocene-catalyzed polypropylene film comprises metallocene-catalyzed ethylene-propylene random copolymer having a melt flow rate of from 10 g/10 min. to 500 g/10 min, wherein the bilayer polymer film does not include a tie layer between the oriented polypropylene film and the metallocene-catalyzed polypropylene film, and wherein the bilayer polymer film has a haze percentage of from 1.5% to 7%.
 17. The method of claim 16, wherein the metallocene-catalyzed ethylene-propylene random copolymer has an ethylene content of from 2 to 10 weight percent, a number average molecular weight of from 5.1×10⁴ to 9.3×10⁴, a weight average molecular weight of from 1.67×10⁵ to 2.20×10⁵, a z-average molecular weight of from 2.98×10⁵ to 4.22×10⁵, a polydispersity of from 2.1 to 3.3, a xylene solubles of from 0.1 to 6.0%, a density of form 0.890 to 0.920 g/cc, and a gloss at 45° of from 70 to
 95. 